Biomacromolecules 2006, 7, 215-223
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The Antithrombogenic Potential of a Polyhedral Oligomeric Silsesquioxane (POSS) Nanocomposite Ruben Y. Kannan,†,‡ Henryk J. Salacinski,†,§ Jaco De Groot,| Ian Clatworthy,# Laurent Bozec,⊥ Mike Horton,⊥ Peter E. Butler,‡ and Alexander M. Seifalian*,†,§ Biomaterials & Tissue Engineering Centre (BTEC), Academic Division of Surgical and Interventional Sciences, University College London, Department of Plastic Surgery, Royal Free Hampstead NHS Trust, London, U.K., Advanced Nanomaterials laboratory (ANL), BTEC, University College London, Birkbeck College, School of Biological and Chemical Sciences Birkbeck College, University of London, London Centre for Nanotechnology and Department of Medicine, University College London, and Electron Microscopy Unit, Royal Free University College Medical School, London, U.K. Received August 18, 2005; Revised Manuscript Received October 9, 2005
We have developed a nanocomposite using a silica nanocomposite polyhedral oligomeric silsesquioxane (POSS) and poly(carbonate-urea)urethane (PCU) for potential use in cardiovascular bypass grafts and the microvascular component of artificial capillary beds. In this study, we sought to compare its antithrombogenicity to that of conventional polymers used in vascular bypass grafts so as to improve upon current patency rates, particularly in the microvascular setting. Using atomic force microscopy (AFM) and transmission electron microscopy (TEM), surface topography and composition were studied, respectively. The ability of the nanocomposite surface to repel both proteins and platelets in vitro was assessed using thromboelastography (TEG), fibrinogen ELISA assays, antifactor Xa assays, scanning electron microscopy (SEM), and platelet adsorption tests. TEG analysis showed a significant decrease in clot strength (one-way ANOVA, p < 0.001) and increase in clot lysis (one-way ANOVA, p < 0.0001) on the nanocomposite when compared to both poly(tetrafluoroethylene) (PTFE) and PCU. ELISA assays indicate lower adsorption of fibrinogen to the nanocomposite compared to PTFE (one-way ANOVA, p < 0.01). Interestingly, increasing the concentration of POSS nanocages within these polymers was shown to proportionately inhibit factor X activity. Platelet adsorption at 120 min was also lower compared to PTFE and PCU (two-way ANOVA, p < 0.05). SEM images showed a “speckled” morphologic pattern with Cooper grades I platelet adsorption morphology on the nanocomposite compared to PTFE with grade IV morphology. On the basis of these results, we concluded that POSS nanocomposites possess greater thromboresistance than PTFE and PCU, making it an ideal material for the construction of both bypass grafts and microvessels.
Introduction The ideal cardiovascular graft, whether a bypass graft or a microvessel, should have the ability to withstand high shear stresses, have similar bulk viscoelasticity to those of the native vessels they are anastomosed to, and, most importantly, possess thromboresistant properties. With decreasing vessel diameters at low-flow states,1 the interplay between these factors is significantly amplified. While results with poly(tetrafluoroethylene) (PTFE) and poly(ethylene terephthalate) (Dacron) are satisfactory in larger vessels, patency is far lower in small* Corresponding author Alexander M. Seifalian, M.Sc., P.G.Dip., Ph.D., F.Int.Nano., Professor of Biophysics & Tissue Engineering & Director of BTEC, Biomaterials & Tissue Engineering Centre (BTEC), University College London (UCL), Rowland Hill, Hampstead, London NW3 2PF, U.K. Tel: ++44 20 7830 2901 (direct). Fax: ++44 20 7472 6444. Email:
[email protected]. † Biomaterials & Tissue Engineering Centre (BTEC), Academic Division of Surgical and Interventional Sciences, University College London. ‡ Department of Plastic Surgery, Royal Free Hampstead NHS Trust. § Advanced Nanomaterials laboratory (ANL), BTEC, University College London. | Birkbeck College, School of Biological and Chemical Sciences Birkbeck College, University of London. ⊥ London Centre for Nanotechnology and Department of Medicine, University College London. # Electron Microscopy Unit, Royal Free University College Medical School.
diameter grafts,2 especially with Dacron, which has high platelet adsorption characteristics.3 In the case of microvessels (
